Roll grooving method and apparatus



JUHY l5, w52 H. E. MULLER, JR 2,603,131

Y ROLL GROOVIG METHOD AND APPARATUS Filed Deo. 14, 1945 I 5 Sheeis-Sheet l July 15, l952 H. E. MULLER, JR 2,603,131

ROLL GROOVING METHOD AND APPARATUS Filed Dec. 14, 1945 5 Sheets-Sheet 2 hweizo: #59AM/v /VUM 59, Je,

July 15, 1952 H. E. MULLER, JR

ROLL GROOVING METHOD AND APPARATUS 5 Sheets-Sheet hfwenl.'

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Filed Dec. 14, 1945 Patented July 15, 1952 UNITED STATES PATENT FFICE BGLL GROOVING METHGD-AND APPARATUS Herman E. Muller, Jr., Youngstown, Ohio, as- Vsignorto United States Steel Company, a corporation of'New Jersey n Application December 14, 1945, Serial o.

This invention relates to a method andan apparatus' for cutting spiralgrooves inthe peripheral surfaces of solids of revolution, for example rolling mill rolls.

` 'The' invention has among its objects the provision of a novel method for the `grooving ofV theperipheral surfaces .of solids of revolution, `suchas rolls, whereby two such rolls are grooved 4at once by the same tool whereby accurate matching ofthe grooves in such rolls isassured` A further object of the invention is /thefpro yision of a simple easily operated Aapparatus .for grooving two rolls at oncelby ythe operation of a single tool. Still 'another object of .the invention is .the provision in such roll grcoving apparatus offmeans ,for feeding the rolls vand .the tool relativetoea'ch otherlin such manner 'that the speed of such .feed is positively correlated -to the relative'speeds of tocl and vrolls Aso that the .desired relationship `between tool and rolls is Ymaintained at all times.

These and other objects of the vinvention Iwill bemore fully apparent the following description of preferred embodiments vof the roll grooving method and apparatus of the .present .invenltion.

ln the rolling of spirally ribbedrods and bars, such as concrete reinforcing bars of Ya typefgenerallysimilar to those disclosed in the patent to Muesery No.' 815,619, it is necessary that at least theflnal set .of rolls be spirally 'grooved soas to present a roll pass having a shape complementary to. that desired in the rod or bar.A Such fmill v'rolls'.are thus grooved circumferentially, such 'c'ircun'fi'fere'ntial .grooves in turn having spiral grooves formed therein, such spiral grooves .lying von a helix whose vaxis is perpendicular yto the 'aids 'of each roll. The spiral grooves, Which must he formed quite accurately to insure :their matching on the mating rolls of the roll pass, have hitherto been dificulty and expensive to form. Use of .the method and .apparatus of the present invention permits the fast accurate forming'of such grooves in two mating rolls at lonev time, therebygreatly speeding 'up' 'the `inachining operation vand at the same vtime insuring V*accurate matching of the spiral grooves on the mating rolls.

'-Brifly, the method consists in placing tvvo previously peripherally grooved rolls together jin Ather'elationshir'they will have in the rolling v`mill and'rotating them in opposite directions at va given-speed. Anelongated cutting tool With-spirally-a'rranged teeth is then -fed centrally intofa vgrooveonithe iii-feed side at right angles to .the

9 Claims. (Cl.V 90-20) 2 plane containing the roll axes. The cutter is rotated at a speed such that the pitch of' its teeth multiplied by its angular velocity equals the in-ffeed velocity plus the peripheral velocity ofthe rolls at the pitch circumferenceA of' the groove, that is, on a circle having a. diameter equal to the pitch diameter of thegroova 'Feeding of the cutter relative to the rolls` to progressively deepen the spiral grooves is accomf plished .either by making vthe cutter teeth of .increasing height along the length `of the cutter or, vvvlren using a cylindrical cutter, by utilizing solely the generally V-shape 'gap vbetween the rolls at ithe inffeecl side o f the ,pass .to provide such feed as the tool is fed intothe pass'. The tool is fed axially in such' manner ,so that during the period'oi `feeding as well as atall other times the conditizonpitch of cutter times angular velocity equals peripheral speed of the rolls at the pitch circumference of the groove-is maintained. Such condition is assured-by thev appa'- ratus ofthe present invention by theprovision of a differential driving means by which the rolls areV drivenJand by Which the rolls `and tool are fed relatively to each other.

The :invention will be more readily understood by the reference to the accompanying drawings, inwhi'ch: Figure 1 is a/vievvin front elevation oan apparatus lfor spiral grooving one -roll pass `of L'aj-set ojf'rollsr; v

'Figure 2 is a view inside elevation partly in section of such roll grooving apparatus, `the fseetion being taken along Vthe line 'II-II in Figure 1;

Figure Sis a view vin horizontal 'section of the roll grooving'apparatusshown in Figuresl and `2, the lsection being taken `along theline III-III inFigure-Z:

YFigure 4 lisjafvietv in front elevation vof -a'n alternative construction of the apparatus,A ."such jrnodication employing va plurality of cutting tools for'grooving a pluralityof roll passes at once;

Figure'-isfa view in side-elevationofa typical cutting `ltool-employed in the apparatus;

Figure `6`-is a yvievv in cross vsection through rsuch tool, the view lbeingftalzen along the' lline VI-VI in Figure -5;

Figure Tis 'a diagrammatic view of thedriving means and controls vfor the various .parts 'of .'th'e apparatus in that -modi-cationin which fthe Vfeed of ythe tool `relative to the rolls` isvaccomplished automatically;

Ym'odiication-ofy the lroll vgrooving apparatus gin 3 which the feed of the tool relative to the rolls is accomplished manually; and

Figure 9 is a view in elevation of a broken portion of a roll having one peripheral pass forming groove spiral grooved by the apparatus of the present invention.

The roll grooving apparatus of the present invention may conveniently take a form similar to that of a milling machine having a vertically adjustable table upon which the rolls are mounted and an adjustable head above the table upon which the tool is carried and driven. In the modification shown in Figures 1, 2, and 3 the apparatus has a vertical column 2 mounted upon a base as shown, the rear portion of the machine providing a support 4 for the motor driving the tool and rolls. Column 2 is provided with vertical ways 6 on the lower portion on which is mounted the vertically adjustable knee 8 on which in turn is mounted the horizontally adjustable table IU. On the upper part of ways 6 is mounted a vertically movable tool slide I2 which carries on its outer face the tool carrying head I4, from the bottom of which projects a quill carrying the vertically positioned rotatable grooving tool I6. i 'I'he rolling mill rolls I8, previously grooved circumferentially as at I9, are mounted horizontally upon the table between the dead centers 20 and the driven chucks 22 which engage the wobbler ends of the rolls so as to hold them accurately in fixed angular position with respect thereto. The chucks 22 are driven through the medium of the gear box 24, which in turn is driven by the horizontal shaft 26, shown in Figure 3. Shaft 26 isdriven by horizontal shaft 30 extending from the column of the machine, through the medium of bevel gears in gear box 28.

Vertical adjustment of the roll carrying table with respect to the tool is accomplished by means of worm 32 which supports the knee 8 and has screw threaded engagement with the portion 34 of the base of the machine. The tool carrying quill or spindle 36 is rotated by means of horizontal shaft 38 within the head I4 through the bevel gears shown in Figure 7, shaft 38 in turn being driven from vertical shaft 42 by the interposed gears 40, shaft 42 being within the .column 2 of the machine and stationarily positioned with respect thereto, the upper portion of such shaft being splined as shown in Figure 'l to allow the horizontal bevel gear of the gearing 40 to move freely vertically thereon. Thus tool I6 is driven at all times, while freedom of vertical adjustment of slide I2 is preserved.

The means whereby shaft 42 driving the tool, shaft 30 driving the rolls, and screw 32 adjusting the table, are driven in the desired relationship may conveniently be assembled in one unit 44, shown at the base of the column 2 and indicated within the dotted lines in Figure '7. From such unit there project the two vertical shafts, shaft 42 previously mentioned, and the vertical shaft 46, to the latter of which is connected the horizontal shaft 30 by means of the gears 48 and 50 shown in Figure 7, gear 5D being splined to shaft 30 and gear 48 being splined to shaft 46. It will be understood that although shafts 30 and 46 are shown parallel to each other in the diagrammatic view in Figure 7 they actually have the relationship indicated in Figures 2 and 3. The gears are so mounted that gears 48 and 50 move vertically with the knee, and that the shaft 30 moves horizontally with the table, there- .by preserving the drive while allowing vertical and horizontal adjustment of the table. Shaft 56 projecting from drive unit 44 drives the knee adjusting worm 32 by means of bevel gears 52 and 54, as shown, gear 52 being splined to the lower unthreaded cylindrical end of the worm shaft as shown to allow vertical movement of the worm with respect thereto. Table I0 is adjusted horizontally by the means shown in Figures l and 2, which comprises a crank 58 on the knee driving horizontal shaft 60 on the inner end of which is carried gear 62 which meshes with the bevel gear 64 keyed to the horizontal adjusting screw 66 for the table. By means of such adjustment of the table the rolls may be positioned with the particular pass thereof to be machined in line with the axis of the tool, which is raised during such adjustment. The motive power for driving unit 44 is provided by motor 68 through belt 10, shown in Figures 2 and 3.

A modification of the apparatus above described is shown in Figure 4. This modification provides a plurality of tools for grooving a plurality of circumferential grooves of a roll set simultaneously. The arrangement of parts in such alternative structure is generally similar to that shown in Figures l, 2, and 3, and similar parts in the two modifications are labeled with the same reference characters. In such latter modification, however, a wider column 'I2 is employed having ways I4 thereon, upon which is mounted the vertically adjustable slide 16. Such slide is provided with the horizontal ways 'I8 upon which are mounted a plurality of tool carrying heads driven from a common horizontal drive shaft, but having splined connections therewith to allow their horizontal adjustment. The horizontal adjustment of heads 80 to bring the axis of each tool in line with a pass of the rolls may be accomplished manually, after which the heads may be locked in position by means not shown. In Figure 4 however, there is indicated a horizontal adjusting screw 82 provided with a crank 84 mounted on the end of slide 16. A retractable split nut, not shown, may be provided on the rear of each head 80 selectively to engage the feed screw 82 so that one or all of the heads may be adjusted by the turning of screw 82, following which the heads are locked in position as described.

A typical tool for use in the present roll grooving method and apparatus is shown in Figures 5 and 6. The tool, which is somewhat similar to a tap, is of elongated shape having a shank 86, a rear portion of reduced diameter 88 for engagement by the tool holding chuck on the quill, and a forward cutting end having spirally arranged cutting teeth thereon. The forward end 90 of the cutting portion is in the form of a smooth right circular cylinder which is somewhat smaller 1n diameter than the pass formed of the peripheral grooves on the rolls. Portion 90 thus functions to guide the cutting portion into the pass and to center it with respect thereto. In the modification of the tool shown, the central core or body of the cutting portion rearwardly of guide 96 is gradually tapered so that it increases in diameter uniformly in a direction toward the shank until it reaches a diameter adjacent the tool shank, which is only slightly smaller than the diameter of the roll pass prior to being grooved spirally. The tool is provided in its cutting portion with a plurality of longitudinally extending fiutes 92 providing spaces for the reception of chips and the introduction of coolant and lubricant. The lands between the flutes are .a timing switch vSwitch |28, which is normally open, when closed clessthe circuit from electrical'mains Li-and Lz provided with a series of spaced teeth 94 of a height from the tool body gradually increasing ktoward the shank, consecutive teeth being vso located ,thatr they lie on a single helix of constant pitcher lead. The teeth have the cross sectional .shape shown in Figure 6, with a forward substantially radial cutting edge 96, and a curved rear edge 08 merging into the side of the adjacent krearwardly located flute. The gradual taper of the cutting section of the tool allows the grooves cut by teeth Si to be deepened gradually asfthe tool is fed axially relative to the rolls. Itis toibe understood, however, that the tool body ofthe cutting section of the tool may be made cylindrical, with `the teeth all of'thesame height, `if dea sired, the generally V formation of the entering portion of the roll pass being relied upon to .provide such increasing depth of cut as the tool and rolls are fed toward each other. It should also be understood that whereas the teeth 'in the cutter shown while on a single helix, they may, if

desired, lie on two or more parallel helices in the manner of ay plural thread. .Figure 9 shows a .spirally grooved` roll out by the tool shown in Figures 5 and 6. As there shown, the tool cuts --a series of parallel grooves 2| `corresponding of contact between them and the cutter-is maintained at all timeswill be more readily apparent by consideration of Figure '7. As there shown, motor .08 drives the main drive shaft of unit through the belt 70. Driven in turn by shaft lili) in fixed relationship thereto is the driving shaft |02 of the timing switch, subsequently to be described, and the shaft |04 driving the cage |08 of a differential. One of the differential branch shafts |08 is connected to the roll driving shaft through the medium of change speed gears H0, the other branch shaft |I2 of the `differential driving knee adjusting shaft through the medium of change speed gears H0. The .tool driving shaft 62 is driven directly off shaft |00, as shown. Shaft |08 is provided with a brake drum IS cooperating with which is the brake H8 actuated by solenoid |20. In the nor- -mal operation of the device,rexcept during feeding of the rolls relative to the tool, the brake |8 is held in released position allowing shaft |03 to Vrotate freely.

Shaft I2 is provided with a similar brake drum |22, cooperating with which is a brake |24 actuated by solenoid IZG. During normal operation of theV device, except during feed of the rolls relative to the tool, brake |211 engages drum |22 holding shaft I2 from rotation. During those intervals, however, atwhich the tool and rolls are fed toward each other the position of the brakes is reversed, `that is, brake H8 engages drum ||6 and brake |24 is released from drum |22, thereby stopping rotation of the rolls and turning the feed screv.r 32 the desired amount to provide an increment of feed of the tool relative to the rolls.

In the modification shown in Figure '7, such relative feed of rolls and tool is accomplished automatically, at regular intervals, by means of |20 actuatedv by shaft |02.

tozthe solenoids |20 and |26, which are connected in parallel. 'Switch |28 is closed whenever the cam |32, driven by shaft |02, is broughtto such angular .position that the raised portion |34 engages 'the Vcam follower |36, thereby closing Ythe switch. W hen such condition occurs'solenoid |20 is energized to apply brake H8 and solenoid 12.6 is, energized to release brake |24. The 'duration lof ,the feeding .period may readily `be changed by the substitution of a cam |32 having a raised portion |34 of .different length. f f

fThexmechanism shown .inFigure f7 therefore permits the .spiral groovingof a peripherally grooved roll .pass to be carried-out automatically,

`once the'proper change speed gears l0 and ||l| are chosen from a consideration of the Ditch of the cutter, .the pitch diameter of thev rolls at 4the peripheral groove, and the pitch of the knee vfeeding screw 32. The properties of the differential drive are such that although the rolls are momentarily halted from rotation during the feeding .periodgthe `feed of the'rolls relative to the .toolby screw 32 is such as .to compensate for .such stoppage ofthe rolls. The differential also allows vthe exact correlationof peripheral speed of the rolls at the pitch circumference `at the point of contact of the tool with the Value of the pitch of the .cutter `times its angle of velocity during those periods in whichY the roll driving shaft |08 is' being decelerated by brake H3 andthe knee adjusting shaft i2 is being accelerated by release of lbrake |24, and during which shaft |08 is accelerated by release of brake ||8 and shaft l2 is being decelerated by operation of brake |2i.

.Such results follow from the fact that the sum of the angular velocities of shafts |08 and ||2 is always twice that of shaft 04, a fundamental Vcharacteristicof a differential. Thus, when shaft |2. is held against rotation the velocity of shaft |00 is twice that of shaft |0ll, and when shaft |03 is held and shaft |2 rotates, the angular velocity .of shaft ||2 is twice that of shaft |04. Accordingly, by a proper choice of the pitch of the knee adjusting screw 32 and of change speed gears I0 vand .HA the upward feed of the rolls will'compensate. at any time during the feeding of the rolls relative vto the tool for the deceleration, stoppage, and acceleration of the rolls H3, thereby allowing the cutter to rotate continuouslyin operative cutting engagement with the rolls without harm'to the rolls or to the cutter.

InFigure 8 there is shown a modification of the device shown in Figure '7, similark parts. in

Figure 8 being designated in the same manner as in Figure '7. In this modification, feed ofthe rolls relative to the cutter is eifected manually and so the shaft |02 and the timing switch driven thereby are omitted. The brake drum, brake: and brake operating solenoid employed on shaft |08 of the first modification are likewise omitted, there being employed, however, Within driving unit 44 a brake drum |22 on shaft H2, a brake |24', and a solenoid |26 which allows the brake to engage the drum when deenergized, but which retracts it from the drum and allows Vshaft ||2 to rotate when it is energized. Energ-ization of I.solenoid |26' from source L1 and Lz is effected when manually operated switch y|38 is closed, thereby connecting wire |40 from the solenoid to the main L2. In this modification the rolls are not stopped during feed of theV rolls relative to the cutter, butinstead, due to the inherent properties of the differential drive, as abovevexplained, will be slowedin rotation at all times in amounts exactlyr sufiicient tocompensate for the ,upward 7 feed of the rolls by the knee screw 32, thereby maintaining the desired relationship between rolls and cutter.

Having thus fully described preferred modifications of the roll grooving method and apparatus of the present invention I desire to claim as new the following.

I claim:

1. Apparatus for spirally grooving the peripherally grooved surfaces of two rolling mill rolls simultaneously, which comprises means for positioning the two rolls with their axes in a common plane and the peripheral grooves mating to form a pass, means for positioning a spirally toothed cutting tool with its axis centrally of the pass and at right angles to the plane of the roll axes, means for rotating the rolls in opposite directions, means for rotating the cutting tool, means for feeding the cutting tool and the rolls relatively toward each other in a direction along a line coinciding with the axis of the tool, a differential device having a cage and two differentially ldriven branch shafts, means for driving the cage thereof in fixed speed relationship to the speed of rotation of one of the two elements consisting of the cutting tool and the rolls, means connecting one branch shaft of the differential to the other of the two elements consisting of the cutting tool and the rolls, and means connecting the other branch shaft of the differential to the means for feeding the cutting tool and rolls relatively toward each other.

2. Apparatus for spirally grooving the peripherally giooved surfaces of two rolling mill rolls simultaneously, which comprises means for positioning the two rolls with their axes in a common plane and the peripheral grooves mating to form a pass, means for positioning a spirally toothed cutting tool with its axis centrally of the pass and at right angles to the plane of the roll axes, means for rotating the rolls in opposite directions, means for rotating the cutting tool, means for feeding the cutting tool and the rolls relatively toward each other in a direction along a line coinciding with the axis of the tool, and a differential device having a cage and two differentially driven branch shafts, means for driving the cage thereof in fixed speed relationship to the speed of rotation of one of the two elements consisting of the cutting tool and the rolls, means connecting one branch shaft of the differential to the other of the two elements l consisting of the cutting tool and the rolls, means connecting the other branch shaft of the differential to the means for feeding the cutting tool and the rolls relatively toward each other, means to brake the feeding means to hold the rolls and cutting tool in fixed relation to each other along the axis of the cutting tool, and means to release said brake to feed the rolls and cutting tool relatively toward each other.

3. Apparatus for spirally grooving the peripherally grooved surfaces of two rolling mill rolls simultaneously, which comprises means for positioning the two rolls with their axes in a` common plane and the peripheral grooves mating to form a pass, means for positioning a spirally toothed cutting tool with its axis centrally of the pass and at right angles to the plane of the roll axes, means for rotating the rolls in opposite directions, means for rotating the cutting tool, means for feeding the cutting tool and the rolls relatively toward each other in a direction along a line coinciding with the axis of the tool, and a differential device having a cage and two differentially driven branch shafts, means for driving the cage thereof in fixed speed relationship to the speed of rotation of one of the two elements consisting of the cutting tool and the rolls, means connecting one branch shaft of the differential to the other of the two elements consisting of the cutting tool and the rolls, means connecting the other branch shaft of the differential to the means for feeding the cutting tool and rolls relatively toward each other, means to brake the feeding means to hold the rolls and cutting tool in fixed relation to each other along the axis of the cutting tool, said braking means comprising a normally operative brake and a solenoid for releasing the braking means, and a switch operable to close the solenoid energizing circuit to release the braking means to allow the rolls and cutting tool to feed relatively toward each other.

4. Apparatus for spirally grooving the peripherally grooved surfaces of two rolling mill rolls simultaneously, which comprises means for positioning the two rolls with their axes in a common plane and the peripheral grooves mating to form a pass, means for positioning a spirally toothed cutting tool with its axes centrally of the pass and at right angles to the plane of the roll axes. means for rotating the rolls in opposite directions, means for rotating the cutting tool, means for feeding the cutting tool and the rolls relatively toward each other in a direction along a line coinciding with the axis of the tool, and a differential device having a cage and two differentially driven branch shafts, means for driving the cage thereof in fixed speed relationship to the speed of rotation of one of the two elements consisting of the cutting tool and the rolls, means connecting one branch shaft of the differential to the other of the two elements consisting of the cutting tool and the rolls, means connecting the other branch shaft of the differential to the means for feeding the cutting tool and rolls relative toward each other, normally operative means to brake the feeding means to hold the rolls and cutting tool in fixed relation to each other along the axis of the cutting tool, normally inoperative means to brake the means connected to the other branch shaft of the differential, and means for simultaneously releasing the first braking means and for applying the second braking means, whereby the rolls and cutting tool are fed relatively toward each other.

5. Apparatus for spirally grooving the peripherally grooved surfaces of two rolling mill rolls simultaneously, which comprises means for positioning the two rolls with their axes in a common plane and the peripheral grooves mating to form a pass, means for positioning a spirally toothed cutting tool with its axes centrally of the pass and at right angles to the plane of the roll axes means for rotating the rolls in opposite directions. means for rotating the cutting tool, means for feeding the cutting tool and the rolls relatively toward each other in a direction along a line coinciding with the axis of the tool, and a differential device having a cage and two differentially driven branch shafts, means for driving the cage thereof in fixed speed relationship to the speed of rotation of one of the two elements consisting of the cutting tool and the rolls, means connecting one branch shaft of the differential to the other of the two elements consisting of the cutting tool and the rolls, means connecting the other branch shaft of the differential to the means for feeding the cutting tool and rolls relatively toward each other, normally operative means to brake the feeding means to hold the rolls and cutting tool in fixed relation to each other along the axis of the cutting tool, normally inoperative means to brake the means connected to the other branch shaft of the diierential, control means driven in timed relationship with the cutting tool, and means responsive to the control means for periodically simultaneously releasing the first braking means and for applying the second braking means, whereby the rolls and cutting tool are fed relatively toward each other.

6. Apparatus for spirally grooving the peripherally grooved surfaces of two rolling mill rolls simultaneously, which comprises means for positioning the two rolls with their axes in a common plane and the peripheral grooves mating to form a pass, means for positioning a spirally toothed cutting tool with its axes centrally of the pass and at right angles to the plane of the roll axes, means for rotating the rolls in opposite directions, means for rotating the cutting tool, means for feeding the cutting tool and the rolls relatively toward each other in a direction along a line coinciding with the axis of the tool, and a differential device having a cage and two differentially driven branch shafts, means for driving the cage thereof in fixed speed relationship to the speed of rotation of one of the two elements consisting of the cutting tool and the rolls, means connecting one branch shaft of the differential to the other of the two elements consisting of the cutting tool and the rolls, means connecting the other branch shaftV of the differential to the means for feeding the cutting tool and rolls relatively toward each other, normally operative means to brake the feeding means to hold the rolls and cutting tool in xed relation to each other along the axis of the cutting tool, normally inoperative means to brake the means connected to the other branch shaft of the diiferential, solenoids for operating the rst and second recited braking means, a circuit for energizing the solenoids, and a switching means in the circuit driven in timed relationship with the cutting tool periodically to operate the solenoids to release the first braking means and to apply the second braking means, whereby the rolls and cutting tool are fed relatively toward each other.

7. The method of spirally grooving a cylindrical body Whose outer surface contains a peripheral groove, which comprises rotating a helically toothed tapered cutting tool in the peripheral groove so as to contact the surface thereof, rotating the body on its axis, the axis of rotation of said tool being parallel to a tangent of the body at the point of contact, intermittently relatively feeding said body and said tool toward each other in a direction parallel to the tool axis while maintaining continuity of cutting and while the tool axis remains fixed, and slowing the rate of rotation of said body to compensate for said intermittent relative feeding, thereby maintaining constant the relative velocity component of the tool teeth in the direction of the tool axis with respect to the body surface at its pitch circumference, said relative velocity component being a summation of velocities which are derived from the helix lead of the rotating cutting tool, rotation of the body about its axis at a varying rate,

and relative feeding between the tool and the body at a varying rate.

, 10 8. The method of spirally grooving a cylindrical body whose outer surface contains a peripheral groove, which comprises rotating a helically toothed tapered cutting tool in the peripheral groove at a substantially constant rate so as to contact the surface thereof, rotating the body on its axis, the axis of rotation of said tool being parallel to a tangent of the body at the point of contact, periodically relatively feeding said body and said tool toward each other in a direction parallel to the tool axis while maintaining continuity of cutting and while the tool axis remains fixed, and decreasing the rate of lrotation of said body during periods of rela-tive feeding to compensate for the relative movement between the tool and the body caused by such feeding, thereby maintaining constant the relative velocity component of the tool teeth in the direction of the tool axis with respect to the body surface at its pitch circumference, said relative velocity component being a summation of velocities which are derived from the helix lead of the rotating cutting tool, rotation of the body about its axis at a varying rate, and periodic relative feeding between the tool and the body.

9. Apparatus for spirally grooving a cylindrical body whose outer surface contains a peripheral groove, which comprises means for rotatably mounting tliebody, a helically toothed rotatably mounted tapered cutting tool adapted to contact the body within the peripheral grooves with the tool axis centrally of the groove and parallel to a tangent of the body at its point of contact, a drive mechanism connected to said tool for rotating the latter, a differential connecting said drive mechanism and the mounting means for the body for transmitting rotary motion to the body, feed means operatively connected to said differential and one of the elements consisting of said tool and the mounting means for the body, means normally holding said feed means stationary and thus preventing feeding, and means for intermittently releasing said feed means and thereby intermittently relatively feeding said tool toward the body while maintaining continuity of cutting, said differential slowing the rate of rotation of the body during each intermittent feed step to compensate for this realtive feeding movement, thereby maintaining constant the relative velocity component of the tool teeth in the direction of the tool axis with respect to the body surface at its pitch circumference.

HERMAN E. MULLER, Ja.

REFERENCES errno The following references are of record in the file of this patent;

UNITED STATES PATENTS Number Name Date 606,837 Gibson July 5, 1898 611,277 Reinecker Sept. 27, 1898 1,705,893 Barnhart Mar. 19, 1929 2,273,050 Kruse Feb. 17, 1942 2,374,254 Zimmermann Apr. 24, 1945 2,416,518 Fields et al Feb. 25, 1947 2,426,774 Jury Sept. 2, 1947 FOREIGN PATENTS Number Country Date y692,128 Germany June 13, 1940 202,925 Switzerland v, May 16, 1939 

